As a structure of positioning and engaging two parts, there is known a structure in which one part has a shaft, the other part has a hole, and the shaft is fitted to the hole. For example, referring to PTL 1, an edge portion of a lower cover has a plurality of pin-like positioning shapes, and an edge portion of a case has a plurality of recessed or protruding positioning shapes. In PTL 1, the edge portions of the case and the lower cover are positioned by fitting the pin-like positioning shapes to the recessed or protruding positioning shapes.